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18 novembre 2013

Bâtiment de terre stabilisée, toiture métallique

Ensemble scolaire au pied de la falaise de Bandiagara (Pays Dogon)

"La structure du bâtiment de l'école se compose d'une véranda prolongée de plus de 3 mètres, parallèles aux salles de classe. Les murs ont été construits en briques de terre comprimée, positionnées de manière alternée, déterminant ainsi le rythme des façades. La véranda est bordée par un muret sur deux côtés délimitant de cette façon la grande terrasse de l'école..."

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Gangaroubourou, LEVS architecten Amsterdam

Project Primary school Architects LEVS architecten Amsterdam Client Foundation Education Dogon, Amsterdam Project organization ADI, Mopti, Sevaré Contractor Enterprise Dara Sevaré, Mopti and executor Essay Dara, in collaboration with students of the Lycée Technique in Sévaré and with the local population of Gangaroubourou Public tender 2012 Construction March – July 2013 Put into service October 2013 Total area 200m2 Terrain 2.5 ha Costs of investment 45.000 Euro

The village of Gangaroubourou is situated on the plain, at more or less an hour driving from the villages at the feet of the rockface in Dogon country, the Falaise of Bandiagara in Mali (World Cultural Heritage, UNESCO, 1986). In this village and in the immediate environment live about 200 families, about 3.500 people. For many years already the village disposes of a traditional school built of clay with a traditional roof. Yet more important is the fact that there is a director and that there are teachers living in houses made by the village. The school accounts about 240 students and continues to grow. Students receiving instruction are to be found from group 1 until group 6. ADI, our local counterpart organization, thinks that this school and this community meet well our most important condition, that is to say, the presence of a motivated community, which could realize jointly with us a new school ensemble, composed of school classes, a school terrain enclosed by trees and toilets.
Although there are already 5 teachers and almost 240 students, we start the first phase with 3 classrooms and sanitary installations. The final ensemble of the school consists of 2 blocks with classrooms for a minimum of 360 students and a maximum of 450. According to our experience, constructing in stages is a wise thing to do. The building project is really workable thanks to the necessary support of the village and this project also partitions the activities of ADI and of SDO.

Simultaneously with the primary school in Tanouan Ibi, the construction of the school building in Gangouroubou has started. On a terrain with a surface of 2,5 ha, the positioning of the classrooms has been determined, taking into consideration factors like the orientation toward the sun, the wind and the underground. The school has been put on the highest part of the ground. That way, water will hardly interfere during the rainy season. The spot for the second block with classrooms has already been reserved on the site (drawing of the spot)

The use of local materials One of the most important points of departure was the use of local resources and materials. The objective here is to get that way to an affordable but sustainable building, fitting well into the landscape and being connected to local and traditional methods of construction. It is true that in the case of this school and on request of ADI we have been using the organization’s stock still available. The idea was also that on the plain, in the most recent villages, another architecture and another presentation of buildings might be possible. For that reason, the school here has been designed with a particular steel roof. The educational process and a committed community As always, it is not the building, but education that is our most important goal. The local contractor and the craftsmen work closely together with those students who just have been educated at the Lycée Technique. They, female and male students, are included in all the stages of the construction process. Prudent steps are set with the objectives of improving and refining the building methods, connecting themselves to already existing methods, traditions and know-how. The local population was mobilized amongst others for digging holes, water supply and for the transport and the piling up of the bricks. It is satisfying to see that the approach of firmer agreements with the villages really works. In any case, our choice to go ahead with building depended on the success of that approach. This way it should also have an impact on the lowering of building costs. Light construction, but nevertheless a pleasant climate In comparison with the schools in Tanouan Ibi or in Balaguina, for the one of Gangaroubouro a new model has been developed. The reason here is, as said before, the stock still available to the foundation. This concerns yet much constructive material, amongst it steel roofs and profiles. After the inventory, Amatigue Dara was also worried about the quality of the soil in the region and he preferred a lighter building. In this case a school building with a floating steel roof.
DESIGN The project consists of an ensemble of the actual school building, blocks with sanitary installations and an exterior communal space. The terrain will be enclosed by Jatropha bushes in order to offer some protection against animals. The oil of the nuts of this plant (‘purging nuts’) will also be used for the manufacturing of biodiesel fuel. The school should comply with the demands imposed by the government and by the CAP (Centre d’Animation Pédagogique). Schools consist normally of blocs with two times three classrooms. A class room should have a surface of 7 x 9 m² and should offer space to about 60 students. In total the school provides space to minimally 180 students and an office with storage facilities for the director, together making up an ensemble. The new model fits better to the open plain, in stead of being close to the local traditional way of building. The villages are also situated out of the richer architectural zone, actually located along the cliff and on the plain. The structure of the school building consists of a prolonged veranda of more than 3 meters, running parallel to the class rooms. The walls have been built in strokes of stones of compressed earth, piled up in an alternating way, and so determining the rhythm of the facades. The veranda is provided with small wall-benches on two sides and shapes this way the big terrace of the school. The roof is constructed of overlapping steel plates, each hanging over and stretching for 1 meter from the veranda and from the facade of the back-part. By means of thin steel shaft profiles, the mass of the roof is being transferred to the buttresses. The Poligny rafters, stretching over the class rooms, create a free floor surface. An advantage of this roof-design, are the large projections, which create additional shady spaces. By means of a wide stroke of `Brazilian´ masonry for ventilation and by the use of several openings of long and narrower windows, we prevent wind forces pushing up the roof from underneath. The facade also causes a lot of natural ventilation in the classrooms. The office and the storage facility have been realized with curved roofs and on a smaller scale, corresponding to the function of the space. The office of the director has also been equipped with a water basin, in which rainwater is caught. The openings in the facades, with its window frames and with blinds, are painted in an ochre yellow color. The floor-stones of 60 mm have been laid down in a decorative pattern, also to make clear that there are many varieties on this point and as a detail of the architecture. The specific place of the teacher in the classroom has been raised, on request of the school, thus increasing class-supervision.
CONSTRUCTING In Dogon country, several building methods are applied, also influenced by the specificities of the location. Clay is the mostly used building material. But also in this case, many varieties prevail, because of the fact that several specimens of clay are available in the Dogon area. In Gangouroubou, clay was the most evident choice in combination with steel with the objective to get a lighter construction. It is very important and as far as possible, to build with locally available materials. Economically and financially this is more interesting than importing materials. It is a more sustainable solution and more over the material is easy to deal with. The whole building, which means the bearing walls and the floors are made of hydraulically compressed earth stones.The stone compressing machine is mobile, which implies that the stones might be produced on the construction site itself, and the bricks might be laid on the same spot with a mortar in which also earth has been mixed. Each stone weighs 8,5 kg and could support a pressure of 15 N-mm². In order to make the stones water resistant, 3 – 4 % cement is added. The foundations are made in poured concrete.The use of wood has been rejected, not only because locally available hard wood is rare, but also because hard wood is very laborious and demanding in terms of maintenance. The frames of the windows are made by craftsmen in Mopti, familiar with the technique. There is still another reason why wood should not be used, and that is the risk of termites, which eat it.

The execution of the construction has been organized by Esay Dara, a bricklayer trained at the Lycée Technique also realized by us. It is fantastic to see the precision in the application of measurements and the preciseness of the masonry during the construction, which is tight and neat, and all this at the same time with a very small loss of bricks. By the way, the whole building-team of this school consists of former students of the Lycée Technique. Also the new generation will produce trained bricklayers and builders. The following pas will be, of course, that they will set off to build yet more based on the own entrepreneurship.

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